Among the devices used for the administration of liquid drugs are portable infusion devices. These infusion devices replace injection with a syringe or with an injection pen.
An example of such an infusion device is an insulin pump for the administration of insulin, such pumps being used in particular by diabetics who are treated with intensified insulin therapy and who measure their blood glucose levels regularly. The insulin pump is carried outside the patient's body, on the belt for example. By means of a thin tube (infusion set or catheter), the cannula of which sits under the patient's skin, the infusion pump delivers a continuous supply of insulin to the body to meet the patient's basal insulin requirement. Additional insulin, such as that required at mealtimes for example, can be supplied by the patient pressing a button.
Infusion devices known from the prior art contain a pump whereby the liquid drug to be administered is pumped from the infusion device. Normally, the infusion device contains a container as a liquid-drug reservoir, from which the drug is displaced by means of a plunger and administered.
Metered dosing of minute quantities of liquid at the microlitre or nanolitre level is becoming increasingly important in many areas of application, e.g. analysis or environmental engineering, as well as medical technology. Pump arrangements that automatically monitor whether the desired quantity of liquid has actually been delivered must therefore be found. Discrepancies between the quantity delivered and the quantity desired can, for example, be caused by a malfunction of the pump or a blockage of the pump passages.